With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras and cellular phones, developments of good secondary batteries, such as lithium secondary batteries, as electric power supply for those devices have been gaining recognition. Further, apart from the technical fields of information-related devices and communication devices, developments of high output and high capacity lithium secondary batteries for electric vehicles and hybrid-power cars as low-emission vehicles have been progressed in other fields such as an automobile industry.
However, since current lithium secondary batteries commercially-supplied use organic electrolyte solutions which have combustible organic media as solvents, attaching of safety systems to prevent temperature rising against short circuit and improvements in their technical structures and materials to prevent short circuit are required.
In contrast, since all-solid-state lithium secondary batteries having their batteries made to an all-solid-state by changing liquid electrolytes to solid electrolytes do not use combustible organic solvents therein, their safety systems are simplified. Accordingly, it is thought that such batteries are good in reducing production costs and in enhancing productivity.
The above-mentioned all-solid-state lithium secondary batteries are produced, for example, by: forming a pellet of three-layer structure of cathode/solid electrolyte/anode by a powder-molding method, inserting the respective battery into a conventional coin-type battery case or a button type battery case, and sealing the periphery thereof. Such all-solid-state lithium secondary batteries tend to have a larger electrochemical resistance and a smaller output current compare to lithium secondary batteries using organic electrolyte solution, because their members constituting the batteries, which are cathode, anode and electrolyte, are all hard solid.
In light of this, it is preferable to use a material having a high ion conductivity as an electrolyte in order to enhance an output current of an all-solid-state lithium secondary battery. Sulfide glasses such as Li2S—SiS2, Li2S—B2S3, Li2S—P2S5 show a high ion conductivity over 10−4 S/cm. Further, a material in which a substance such as LiI, Li3PO4 added thereto also show a high ion conductivity of about 10−3 S/cm. It is thought that these glasses having sulfide as their main constituent show higher ion conductivities compare to those of oxide glasses because sulfide ions are ions having larger polarization compare to oxide ions and sulfide ions have small electrostatic attractive force with lithium ions.
However, with batteries using solid electrolyte materials (sulfide-based solid electrolyte materials) which have the above-mentioned sulfide as their main constituent, there is a risk of leaking hydrogen sulfide gas to the outside of their battery cases when water is entered into the battery cases and the gas is generated. As hydrogen sulfide gas has pungent odor, prevention of the gas leakage to the outside of the battery case is desired.
To respond such desire, a method of providing an adsorbent to inside or outside of a battery case to absorb the gas generated inside the battery is proposed. For example, in the Patent Document 1, hydrogen sulfide gas is absorbed by using adsorbents such as zeolite, silica gel and activated carbon. However, since the adsorbent such as zeolite, silica gel and activated carbon absorb the gas using the surface adsorption, their adsorptive capacity are lost when the surface is covered by a large amount of water or the like. Therefore, there has been a problem of being incapable in preventing the leakage of hydrogen sulfide gas generated because their adsorptive capacity is lowered when a large amount of water is entered into a battery by an accident such as submersion caused by breakage of the container or being exposed to buckets of rain.    Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2004-087152    Patent Document 2: JP-A No. 2004-227818    Patent Document 3: JP-A No. 2003-151558    Patent Document 4: JP-A No. 2001-052733    Patent Document 5: JP-A No. 11-219722    Patent Document 6: JP-A No. 2001-155790